treefmt covers python with ruff-format and ruff-check, ruff in the dev shell

docs/4-implementation/scheduler/ci.md

@@ -129,9 +129,10 @@ Nix interpolation. Commands the script runs in the VM find their binaries on the
 node's `environment.systemPackages`. Build-time values (socket path, forge
 domain, store paths) arrive as `FULL_SETUP_*` environment variables, set in
 `nix/vm-tests/full-setup.nix` through `overrideTestDerivation`. To add a value,
-set one there and read it with `os.environ` in the script. The `ruff (vm-tests)`
-job checks and format-checks `nix/vm-tests/*.py`; `nix/vm-tests/ruff.toml` names
-the globals the test driver provides.
+set one there and read it with `os.environ` in the script. `nix fmt` formats and lints the Python (treefmt's
+`ruff-format` and `ruff-check`, which fixes what it can), and the `formatting`
+flake check fails on a file `nix fmt` would change. `nix/vm-tests/ruff.toml`
+names the globals the test driver provides.
 
 ## Configuration reference
 

docs/5-project/process/conventions.md

@@ -458,7 +458,7 @@ nix fmt                       # treefmt — authoritative, NOT bare cargo fmt
 
 `nix fmt` (treefmt) is the formatter CI gates on; bare `cargo fmt`
 misses the non-rust files treefmt also covers, so always run `nix
-fmt` before pushing.
+fmt` before pushing. It also formats and lints Python with ruff.
 
 **Clippy discipline — never add `#[allow(clippy::…)]`.** All lints are
 CI-fatal at `-D warnings` (pedantic included); every warning that fires